When clouds and mountain peaks intervene or partially shadow the sun's rays, the light is scattered in a parallel direction throughout open spaces in clouds and other places. These rays are called Crepuscular rays. You will most commonly see these rays during sunrise, sunset, and dusty or cloudy days. Depending on when you see them they will appear to be coming from different directions. 
Sunset
Example: During sunset the rays will produce a bottom to top or north to south effect.
http://www.allthesky.com/atmosphere/sunrays.htmlhttp://www.demark.org/essays/CrepuscularRays.htmlhttp://www.chitambo.com/clouds/cloudshtml/crepuscular.html
http://www.astrophys-assist.com/wilobs/weathwin/crepsculr.htm
